1. Field of the Invention
The present invention relates to a semiconductor device and, more particularly, to a contact structure of a semiconductor device using an aluminum layer, and a method for fabricating the same.
2. Description of the Related Art
Reduction in design rule of a semiconductor device has resulted in gradual deterioration of a contact hole filling properties. Accordingly, to effectively fill a contact hole of a high aspect ratio with a fine critical dimension, a method for forming a tungsten contact has been introduced, which employs a chemical vapor deposition (CVD) process to deposit tungsten.
Meanwhile, as an operating speed of a higher level, for example, an operating speed of 667 MHz or more has been required for semiconductor devices, for example, graphic memory devices, reduction of contact resistance has been also required. Because tungsten has a relatively high specific resistance of about 20 μΩcm or more, it has a limit to satisfy the requirement for a lower contact resistance. For example, a contact area of 0.025 μm2 exhibits a considerably high contact resistance of several ohms (Ω).
As a conductive material with a lower specific resistance than that of tungsten, aluminum can be considered. However, when filling a contact hole with an aluminum layer, gases generated from an inter-dielectric layer constituting a side wall of the contact obstruct deposition of the aluminum layer, thereby deteriorating step coverage of the aluminum layer.
FIG. 1 is a cross-sectional view schematically illustrating a conventional method for forming a contact of a semiconductor device.
Referring to FIG. 1, for the conventional contact forming method, an upper dielectric layer 23 is formed to cover a lower wire 30 formed on a lower dielectric layer 21 of a semiconductor substrate 10. Then, a contact hole 25 is formed to penetrate the upper dielectric layer 23, and is filled with an aluminum layer by deposition. Here, the deposition of aluminum (Al) is obstructed by gases discharged from a dielectric material such as BPSG constituting the upper dielectric layer 23, so that the step coverage of the Al layer is deteriorated.
The materials discharged from the upper dielectric layer 23 may include moisture contained therein upon application of BPSG, or compounds which contain boron (B), phosphorus (P) and the like. Such discharged materials are discharged to an outside of the upper dielectric layer 23 at temperatures for deposition.
For BPSG, it is measured that a material having an atomic weight of 18, for example, moisture, is primarily discharged in a large amount within 1 to 4 seconds at a temperature of about 200° C. In addition, it is measured that the material having an atomic weight of 18 is also secondarily discharged in a large amount within 1 to 2 seconds below a temperature of about 300° C., and that the material is tertiarily discharged in a large amount within 1 second at a temperature of about 400° C. although the discharge amount of the material is relatively reduced.
The discharged gases can serve as elements of obstructing deposition of the Al layer, and lead to deterioration in filling property of the Al layer in the contact hole 25. Thus, it is urgently needed to develop a method, which can solve the obstruction of the discharged gases against deposition of the Al layer when forming the contact using the Al layer.